This invention relates to a dental handpiece having a turbine rotatable in reverse direction, whereby a dental tool attached to the handpiece may be driven in forward and reverse directions for dental treatment.
A dental handpiece having attached thereto a dental tool for grinding a tooth or a metal prosthetic material has been used extensively. A driving device such as an impeller driven under an air pressure, a water conduit and air supply/discharge conduits are provided within the inside of the dental handpiece. The dental tool having a grinding tip end is adapted for being rotated by the driving device. In dental treatment, dental tools having a grinding ends suited to the positions or shapes of the sites of treatment or to the objectives of treatment are selected and selectively attached to a tool head such as turbine head.
FIG. 7 is a front view showing a conventional dental handpiece. An air supply conduit 2 and an air discharge conduit 3 are separately formed within a handle part 1 of the handpiece, as shown in FIG. 8, and compressed air is supplied from an air tube 4 into the air supply conduit 2. The air supply conduit 2 and the air discharge conduit 3 are separated from each other by a partition 5 within the handle part 1. A turbine blade 7 is rotatably mounted within a turbine head 6. A central shaft 8 of the turbine blade 7 is rotatably supported by bearings, not shown. A dental tool 9 is attached to the central shaft 8 by, e.g. a chucking unit, not shown, for grinding the tooth or the metal prosthetic material.
With the above-described dental handpiece, compressed air is supplied from the air tube 4 via the air supply conduit 2 to the turbine head 6 so as to impinge via the end of the conduit 2 onto the turbine blade 7 for rotating the turbine blade 7 about the central shaft 8 as the center of rotation. By the rotation of the turbine blade 7, the air is discharged from the space between vanes 7a via the discharge conduit 3. The turbine blade 7 is rotated at an elevated speed by the compressed air to cause rotation of the dental tool 9 in a predetermined direction for grinding the tool.
Meanwhile, as shown in FIG. 9, when the marginal edge of a metal prosthetic material 11 such as an inlay filled in tooth is cut by the above-described dental handpiece, it is preferred that rotation of the dental tool 9 be in a direction of from the metal prosthetic material 11 towards the tooth surface, so that a part of the metal prosthetic material 11 is not extended from the tooth surface, that is, in order to prevent irregularities from being produced on the edges of the metal prosthetic material 11 or to prevent a gap from being produced between the metal prosthetic material 11 and the tooth.
Besides, for adapting the metal prosthetic material 11 to the defect portion of the tooth 12 after removal of the site of lesion in the course of treatment of tooth caries, and for retaining the metal prosthetic material 11 against the biting force, it is necessary to cut a basically rectangular tooth cavity 13 to attach the prosthetic material 11 in the so-formed cavity 13, as shown in FIG. 10. At this time, the fundamental procedure is to rotate the dental tool 9 in a direction proceeding from the tooth towards outside, that is in a direction of flying the debris towards outside, because otherwise a smooth marginal edge cannot be obtained.
However, with the conventional dental handpiece, the direction of flow of compressed air through the air supply conduit 2 and the air discharge conduit 3 is constant, so that the dental tool 9 can be rotated only in one direction. Consequently, for cutting left and right teeth or cutting left and right sides of the same tooth, the edge portions of the tooth cannot be cut from the metal material towards the tooth surface, insofar as one of the teeth or one of the left and right sides of the same tooth are concerned. On the other hand, it becomes impossible from time to time to cut the tooth from the tooth towards outside during formation of the tooth cavity, as a result of which a gap tending to produce secondary caries may be produced between the metal prosthetic material and the tooth or a smooth edge portion cannot be produced by cutting.